Glass fiber mats are used as reinforcing elements for roofing shingles, flooring, and wall coverings, as well as in the formation of molded parts using polymer resins. The fiberglas s mat industry typically uses 1.25 inch fiberglass fibers to make mats. These fiberglass fibers are generally coated with a sizing agent, typically an antistatic compound, such as a cationic softener, and formed into mats.
The two most common methods for producing glass fiber mats from such fibers involves wet-aid and dried processing. Typically, in a dry-lid process, fibers are chopped and air blown onto a conveyor, and a binder is then applied to form a mat. Dry-laid processes may be particularly suitable for the production of highly porous mats having bundles of glass fibers. However, such dry-laid processes tend to produce mats that do not have a uniform weight throughout their surface areas. This is particularly true for lightweight dry-aid mats having a basis weight of 200 g/m.sup.2 or less. In addition, the use of dry-chopped input fibers can be more expensive to process than those used in a wet-laid process, as the fibers in a dry-laid process are typically dried and packaged in separate steps before being chopped, which may not be necessary in wet-laid processes.
In a wet-laid process, an aqueous solution, often referred to in the art as "white water", is formed into which the glass fibers are dispersed. The white water may contain dispersants, viscosity modifiers, defoaming agents or other chemical agents. Chopped, fibers are then introduced into the white water and agitated such that the fibers become dispersed, forming a slurry. The fibers of the slurry may then be deposited onto a moving screen, whereupon a substantial portion of the water is removed-to form a web. A binder is then applied to the web and the resulting mat is dried to remove the remaining water and to cure the binder. The resulting non-woven mat is an assembly of dispersed glass filaments.
The white water and resulting slurry can play a major role in achieving the desired fiber distribution within the glass fiber mats. For example, the type and charge of the glass fibers, the dispersant, and/or the viscosity modifiers in the white water can affect the level of dispersion of the fibers. Further, the level of dispersion of the fibers during processing has a significant effect on the porosity, tensile strength and tear strength of the finished glass mat.
Wet-laid processes have employed nonionic viscosity modifier systems, which may contain a cationic viscosity modifier, or anionic viscosity modifier systems. For example, U.S. Pat. No. 4,869,932 proposes treating glass fibers with low molecular weight watersoluble anionic vinyl polymers for use in a white water having a long-chain anionic viscosity modifier, to prevent precipitates from interfering with the white water formulation. In contrast, U.S. Pat. No. 4,526,914 relates to a white water dispersant system employing a cationic surfactant, a viscosity modifier system having a cationic viscosity modifier and 0 to 90% of a nonionic cellulosic viscosity modifier.
Previous systems have not proven entirely satisfactory for controlling the dispersion of fibers and subsequent formation of glass mats with controlled porosity, particularly for bundled or structured glass mats. For example, wet-laid processes containing an anionic polyacrylamide viscosity modifier have been used to make mats with highly dispersed fibers, such as for roofing mats, but are not suitable for making bundled or structured glass mats.
Accordingly, there is a need for a wet-laid process for making glass mats which is economical and allows better control of fiber-fiber interactions. More particularly, there is a need for an improved wet-laid process for making bundled or structured glass fiber mats having a high porosity and a uniform weight.